The one drop fill (ODF) technology is becoming the mainstream in processes for manufacturing LCD elements (LCD panels), replacing the conventional vacuum injection technology, in order to meet expectations of shortening the manufacturing process time. In an ODF process, LCD elements are produced as follows. First, a sealant is dispensed on an electrode-equipped substrate to form a frame of a display element, and liquid crystals are dropped inside the depicted frame. Next, another electrode-equipped substrate is joined thereto under vacuum. Then, the sealed portions are semi-cured by being irradiated with ultraviolet rays, and are then full-cured by being heated for liquid crystal annealing and heat-curing. This process, which employs two-stage curing consisting of photocuring and heat-curing, can shorten the curing time as well as the overall time for the LCD-element manufacturing process.
The currently-employed seal-curing conditions, however, involve irradiation of ultraviolet rays as well as curing at high temperatures, thus exposing the liquid crystals to both such ultraviolet rays and high temperatures upon seal-curing and greatly damaging them. Thus, the currently-employed conditions do not completely satisfy such needs as supporting the electrooptical properties required of the liquid crystals. Also, there are other problems to be solved, such as the energy cost incurred upon heat-curing and the need for further reduction in processing time. Accordingly, there has been a demand for a curing technique that utilizes visible light, which is not absorbed by the liquid crystals, and that employs a lower heat-curing temperature, with the aim of suppressing degradation of the liquid crystals during the process of curing the sealed portions.
Patent Document 1 discloses the advantages of combining a high-molecular-weight photoinitiator having at least three aromatic rings and a resin composition containing 60% by mol or more of a photocuring functional group. Patent Document 1, however, describes nothing about curing under visible light, nor does it particularly describe the advantages of an acylphosphine-based photoinitiator.
Meanwhile, conventionally-used latent curing agents for epoxy resins include hydrazide-based curing agents and amine adduct-based curing agents. A hydrazide-based curing agent consists of a single compound, and therefore, it is possible to reduce the effect it has on liquid crystal contamination by removing impurities through refining. However, such a hydrazide-based curing agent requires around 1 hour at 120° C. to cure. Accordingly, there is a demand for a curing agent that cures at lower temperatures and in a shorter time to thus simplify the curing process. As regards amine adduct-based curing agents, compounds containing tertiary amino groups are prone to form amine salts, thus having a tendency of inhibiting polymerization and making it difficult to obtain cured resins having good physical properties. On the other hand, compounds containing primary amino groups are prone to cause reaction with epoxy resins, thus having a drawback in storage stability. Patent Document 2 discloses a curing agent that allows curing to take place at curing temperatures of 80 to 100° C. by solving the above-mentioned problem by masking the primary amino groups with an acid substance. Patent Document 2, however, neither teaches nor suggests combining the disclosed curing agent with a photo-curable resin for use as an ODF sealant.